Our objectives in this project have been to examine the details of the interaction of self and antigenic peptides with the MHC class I molecule by detailed kinetic and equilibrium binding methods, and by three- dimensional computer modeling of structures of MHC/peptide complexes. Such studies permit us to examine underlying biochemical rules that govern the interaction of antigenic peptides with MHC molecules, which plays a central role in the initiation of the immune response. In addition, they provide a framework for understanding the larger question of how proteins bind small molecular weight peptide ligands. Major accomplishments in the past year include the further development and application of quantitative kinetic assays for measurement of the interaction of peptides with purified MHC molecules in real time, and the extensive analysis of the binding of a larger number of peptides. In addition, methods have been devised for the quantitative emptying of MHC class I molecules and the retention of their peptide binding activity. In addition, general methods are being developed for the chemical coupling of engineered molecules tagged with histidine residues to metal- conjugated biosensor surfaces.